I have known a certain member of this forum to use what we've named the Stannah Diver lift. I won't tell you who as it's not really reccomended.

With the engine turned off swim round to the back of the boat.
Place one foot on each side of the cavitation plate, reach around to the tilt switch on the side of the engine cowling and use the hydraulics to lift you up to a point where you can step onto the transom.

Unfortunately as the engine tilts forward you usually end up looking like you've become Very friendly with your RIB

Nasher.

Might still be a problem with side tanks.
If it was really rough I'm not sure that I would be too happy on a lift. Might consider kneeling down otherwise I have found myself being thrown all over the place on a lift, even when not too rough.
If diving from a RIB I would prefer to de-kit in the water, just keep your mask on and DV rammed into your eating orifice until the last possible moment

I have a design in my head for one on my RIB. I'll make a S/Steel prototype first the get an Ali one made for lightness and see if it will be strong enough, may have to be SS. It'll be attached to the side of my A frame, which I'll brace to help rigidity although it did support the 179kg engine without bending.

Electric winch mounted low down with a pully at the top, biggest problem is to keep it out of the water while the boat is moving. Folding platform with 'handlebars' for divers to grab.

im also in the process (over the winter) of re engineering a ladder / lift for the RIB. it will be in stainless and be incorporated into the aft ladder set up. Once I get more detail I will post further info.

We've batted this one around at our dive club, a few of us are in engineering in some sort of way. One idea was to incorporate into the tubing of the A frame either cable or chain to a motor in the centre of the top of the a frame. This would drive both sides in/out thus up or down. A platform of some sort could travel up and down this way hey presto a lift.